Fan motors, e.g., for motor vehicles, are typically triggered by a control unit. For continuous triggering, the control unit generates periodic pulse-width-modulated triggering signals for this purpose, using which a field-effect power transistor is triggered. The field-effect power transistor is connected in series with a fan motor, which is connectable to the control circuit, between two supply voltage potentials. The control unit varies a pulse duty factor of the triggering signal, so that the fan motor is controlled continuously.
In a pulse-width-modulated signal, the pulse duty factor specifies the proportion of time in which the signal level is in a high state during a period of the triggering signal. In this case, the high state triggers the field-effect power transistor in such a way that it is conductive and applies the entire supply voltage to the fan motor. During a low level of the pulse-width-modulated signal, the field-effect power transistor is completely blocked, so that the supply voltage is disconnected from the fan motor.
The frequency of the pulse-width-modulated triggering signal is typically in a frequency range which may not result in audible oscillations in the fan motor and/or in the triggering electronic system.
Faults may occur during the installation and operation of the fan motor, which may typically not be easily recognized.